Shields, who qualifies for England through his parents, will join English club side Wasps after Super Rugby ends in August, prompting speculation that he could play a part in the three tests in South Africa.
British media have reported that 27-year-old will be available for selection, despite still being contracted to New Zealand Rugby and having a number of Hurricanes matches to play after June.
NZR chief executive Steve Tew begged to differ.
"I don't think you should jump to the conclusion that he will be available from our point of view," Tew told the New Zealand Herald on Thursday.
"He has signed to New Zealand and he is contracted to play for New Zealand teams until the end of Super Rugby."
The Hurricanes have three regular season games and up to three playoff matches after the June international window.
NZR granted a release to England-born flyhalf Piers Francis for last year's tour of Argentina in June, excusing him from an Auckland Blues game before he linked up with English side Northampton.
Shields, however, was a New Zealander, Tew said.
"We have a New Zealand player who is contracted to be here until the end of that competition and that would be our expectation," Tew added.
"We are obligated to release players who have signed to play for other countries so they have made themselves unavailable for New Zealand.
"We always make sure that occurs and that is of particular relevance to the Pacific countries.
"But in this instance, Brad has signed a contract that makes him available for New Zealand teams."
(Reporting by Greg Stutchbury; Editing by Ian Ransom)
